Method for regulating or controlling the temperature of a glow plug

Abstract

Method for regulating or controlling the temperature of a glow plug in a heating phase of the glow plug (2), in which a temperature value is determined as a function of a resistance of the glow plug (2), wherein the heating phase follows a preheating phase, wherein during the preheating phase the cold glow plug (2) is subjected to a heating voltage which is higher than the operating voltage provided for the glow plug (2), whereby a non-stationary temperature profile is formed in the glow plug (2), characterized in that the temperature value (T mod ) depending on a measured resistance (R mess ) and a calculated resistance value (ΔR(t K )) it is determined that the calculated resistance (ΔR(t K )) to determine the temperature value (T mod) during the transient temperature profile within the glow plug (2) is calculated using a physical model, so that the temperature value (T mod ) is determined at several time intervals (k), whereby the calculated resistance value (ΔR(t K )) changes depending on the previous time intervals (k-1), that the calculated first resistance value (ΔR(t 0+1 ))with a starting value (ΔR(t t=0 )) is initialized so that the starting value (ΔR(t T=0 )) from a difference of a resistance (R t=30 ), which is determined once based on a homogeneous temperature distribution in the glow plug, and a resistance detected after the preheating phase (R push(t=0 )), where the calculated resistance value (ΔR(t K )) is determined as a function of a decreasing exponential function, where the exponents depend on the thermal relaxation time (t K) and a time constant (τ) and that the time constant (τ) is determined once for the respective glow plug (2) used.

Description

State of the art

[0001] The invention relates to a method for regulating or controlling the temperature of a glow plug in a heating phase of the glow plug, in which a temperature value is determined as a function of a resistance of the glow plug.

[0002] Glow plugs, which are used in internal combustion engines to ignite a fuel-air mixture, are preheated when cold, before their temperature is high enough to ignite the fuel-air mixture. The glow plug has a heater that applies an excessive heating voltage to the cold glow plug for a short period of 1 to 2 seconds, so that the glow plug is overloaded at this time. After this so-called push phase, the tip of the glow plug has reached a temperature of over 1000°C, while the rest of the glow plug is still at a temperature well below 1000°C.

[0003] Normal regulation or control of the glow plug is achieved by measuring the resistance of a glow wire inside the glow plug. Since the remainder of the glow plug, and thus also the remainder of the glow wire, has not yet reached the temperature of the glow plug tip after the push phase, normal temperature regulation or control via measuring the glow wire resistance is not possible. The transient temperature curve that has established itself in the glow plug after the push phase lasts for approximately 30 seconds. After this time, the temperature in the glow plug has stabilized, so that normal temperature regulation or control via the measured resistance is possible.

[0004] DE 10 247 042 B3 discloses a method for controlling the heating of the glow plugs of a diesel engine, in which the thermal behavior of the glow plugs during heating and cooling is emulated and the temperature feedback of the emulation is used as a control variable for controlling the heating of the glow plugs.

[0005] DE 10 2006 025 834 A1 discloses a method for controlling a glow plug in a diesel engine, in particular in the preheating phase, in which the temporal gradient of an electrical variable occurring at the glow plug as a function of temperature is measured, compared with a limit value and, if the limit value is exceeded or undershot, the electrical supply voltage of the glow plug is changed. Disclosure of the invention

[0006] The invention is based on the object of specifying a method for regulating or controlling the temperature of a glow plug in a heating phase of the glow plug, in which the regulation or control of the temperature of the glow plug is also possible during a transient temperature distribution within the glow plug.

[0007] According to the invention, this problem is solved by calculating the resistance to determine the temperature value during a transient temperature profile within the glow plug using a physical model. The advantage of the invention is that the glow temperature is modeled with high accuracy, thus allowing the glow temperature to be regulated or controlled at any time during the glow phase, especially directly upon starting the combustion engine.

[0008] Advantageously, the temperature value is determined based on a measured resistance and a calculated resistance value. The measured resistance provides a reliable starting point for calculating the temperature values, which are calculated during the heating phase. This ensures that the temperature values determined during the heating phase using the calculated resistance values form a reliable basis for regulating or controlling the glow temperature of the glow plug.

[0009] The temperature value is determined at multiple time intervals, with the calculated resistance value changing depending on the previous time intervals. This means that after each specific time interval, a new temperature value is calculated, which forms the basis for the regulation or control. The resistance value to be calculated advantageously depends only on the elapsed time interval and not on the previously determined temperature, which is particularly advantageous in the case of a transient temperature profile, such as that encountered during the heating-up phase of a glow plug. This approach eliminates the need for applications that use a thermocouple as a measuring plug, thereby reducing material costs.

[0010] The first resistance value to be calculated is initialized with a start value.

[0011] The starting value is determined from the difference between a resistance, which is determined once based on a homogeneous temperature distribution in the glow plug, and a resistance detected after the preheating phase has ended. It is assumed that the time at which the preheating phase ends, also known as the push phase, is the same time as the start of the temperature equalization phase, known as the heating phase. Thus, the difference is calculated from the resistance expected after the end of the heating phase and the resistance that occurs after the preheating phase has ended at the start of the heating phase.The calculation of the resistance after completion of the heating phase depends on the temperature reached by the glow plug after the preheating phase and is calculated from the energy provided by the glow plug, taking into account the vehicle voltage to which the glow plug is connected.

[0012] The calculated resistance value is determined as a function of a decreasing exponential function, where the exponents are formed by the thermal relaxation time and a time constant. The thermal relaxation time is the time until the glow plug temperature has stabilized after the push phase, i.e., the glow plug has reached a steady-state temperature distribution. Such transient modeling of the glow plug temperature during the warm-up phase enables engine operating point-dependent glow temperature control and regulation, for example, by adjusting the engine load differently.

[0013] The time constant is determined once for each glow plug used. Since the time constant is glow plug-specific due to production variations, the time constant is determined immediately after the glow plug is installed in the combustion engine and is stored in a control unit for future use.

[0014] In one variant, the starting value is multiplied by the exponential function.

[0015] In a further development, during the brief preheating phase, the cold glow plug is subjected to a heating voltage that is higher than the operating voltage intended for the glow plug, resulting in the transient temperature profile in the glow plug. This procedure brings the glow plug to a temperature that causes the transient temperature profile in the glow plug and where the physical model for determining temperature conditions during the heating phase of the glow plug is applied, in which the transient temperature distribution changes to a steady-state temperature distribution along the glow plug.

[0016] Advantageously, the resistance value calculated for a previous time period serves as the starting point for calculating the next resistance value in the following time period. The calculated resistance values build on each other, allowing the physical model to accurately represent the transient temperature profile of the glow plug, both in still air and during engine start-up or idling, as well as during dynamic engine operation when the vehicle accelerates immediately after starting. Therefore, the temperature values calculated using the physical model can be used to regulate or control the glow plug temperature.

[0017] In one embodiment, the resistance of the glow plug is measured to determine the temperature value after the preheating phase has ended.

[0018] In one variant, the measured resistance is determined from a voltage and a current, which are determined by measuring the voltage applied to the glow plug and the current flowing through it. Since these parameters can be measured using the control unit, the resistance can be easily calculated from the actual state of the glow plug. However, due to the unsteady temperature distribution, the resistance will be lower than the resistance expected after the warm-up phase.

[0019] Advantageously, after the glow plug's heating phase, during which a steady-state temperature profile has been established, the temperature is controlled based on a measured resistance value that represents the glow plug temperature. This allows the glow plug temperature to be controlled and regulated at any time from the start of the combustion engine, since the actual temperature value is determined using the physical model during the transient temperature profile. After the steady-state temperature profile has been established, the glow plug's resistance is measured, and the actual temperature values for the closed-loop and / or open-loop control are determined from this.

[0020] The invention permits numerous embodiments. One of these will be explained in more detail with reference to the figures shown in the drawing.

[0021] It shows: Fig. 1: Schematic diagram of the arrangement of a glow plug in an internal combustion engine Fig. 2: Schematic flow diagram for calculating the temperature during the unsteady temperature distribution.

[0022] Cold combustion engines, especially diesel engines, require starting assistance at ambient temperatures below 40°C to ignite the fuel-air mixture introduced into the diesel engine. Glow systems are used as starting aids. These consist of glow plugs, a glow time control unit, and glow software stored in an engine control unit. Glow systems are also used to improve vehicle emissions. Other applications for glow systems include burner exhaust systems, auxiliary heating, fuel preheating (flex fuel), and coolant preheating.

[0023] Fig. 1 shows such a glow system 1. A glow plug 2 protrudes into the combustion chamber 3 of the diesel engine 4. The glow plug 2 is connected, on the one hand, to the glow time control unit 5 and, on the other hand, to an on-board voltage 6, which controls the glow plug 2 with the nominal voltage of, for example, 11 V. The glow time control unit 5 is connected to the engine control unit 7, which in turn leads to the diesel engine 4.

[0024] To ignite the fuel-air mixture, the glow plug 2 is preheated by applying an overvoltage in a push phase lasting 1 to 2 seconds. The electrical energy thus supplied to the glow plug 2 is converted into heat in a heating coil (not shown in detail), causing the temperature at the tip of the glow plug to rise sharply. The heating output of the heating coil is adjusted to the requirements of the respective diesel engine 4 via the electronic glow time control unit 5. The fuel-air mixture is guided past the hot tip of the glow plug 2 and heats up in the process. Combined with intake air heating during the compressor stroke of the diesel engine 4, the ignition temperature of the fuel-air mixture is reached.

[0025] The glow plug 2 has various glow phases. As already described, in a preheating phase, the push phase, which lasts 1 to 2 seconds, a push voltage is applied to the cold glow plug 2, which is above the nominal voltage of the glow plug 2. During this short period of time, the tip of the glow plug is heated to approximately 1000°C, while the remainder of the glow plug 2 remains below this temperature, resulting in a transient temperature profile within the glow plug 2. This preheating phase is followed by a heating phase of the glow plug 2, in which the transient temperature distribution balances out to a steady temperature distribution across the entire glow plug 2. Such a heating phase normally lasts approximately 30 seconds.During this period, the temperature of the glow plug 2 is not available for control and / or regulation by the engine control unit 7 containing the software for the glow function. According to the state of the art, the glow function could only be controlled after the steady-state temperature profile of the glow plug 2 had been established.

[0026] In Fig. 2 shows a schematic flow diagram for calculating the temperature during the heating phase, which is integrated as software in the engine control unit 7 and is taken into account there in a temperature control of the glow function of the glow plug.

[0027] In block 100, the energy of glow plug 2 is determined by measuring the vehicle's electrical system voltage and the current, which is powered by diesel engine 4. The duration of the push phase is determined based on this electrical system voltage. Subsequently, in block 101, the temperature TPush which the tip of the glow plug 2 has reached due to the energy made available to the glow plug 2 during the push phase in the form of the push voltage.

[0028] Based on these assumptions, a resistance difference ΔR (t=0) calculated. ΔR(t=0)=R(t=30)−RPush(t=0)

[0029] Alternatively, the resistance values can be converted directly into a temperature. Then the following applies: ΔT(t=0)=t(t=30)−TPush(t=0) where T(t=30)=f(R(t=30)) and TPush(t=0)=f(RPush(t=0)).

[0030] The measurement of the resistance value R (t=30) This is done once after the installation of the glow plug 2 in the diesel engine 4, assuming a steady-state temperature distribution, and is saved for further calculations. Alternatively, the resistance value R (t=30)be calculated from a resistance model which determines the resistance value R (t=30) as a function of the temperature T reached in the push phase Push of the glow plug 2, where, as already explained, the temperature T Push is a function of the energy provided in the push phase of glow plug 2.

[0031] In block 103, the temperature equalization process taking place in the heating phase following the push phase is modeled using an exponential approach, taking into account the thermal relaxation time t. Tmod=f(Rmess)+ΔR(tK)

[0032] When converting to a temperature, the following applies: Tmod=Tact+ΔT(tK), where Tact=f(Rmess) where ΔR(tK)=f(exp(−dtK / τ) or ΔT(tK)=f(exp(−dtK / τ).

[0033] A resistor R messwhich is applied to the filament of the glow plug at a time t0. For this purpose, the voltage applied to the filament of the glow plug 2 and the current flowing through the glow plug are measured, and the resistance R mess calculated.

[0034] The time t0 represents the end of the push phase but also the beginning of the temperature equalization process, i.e. the heating phase.

[0035] An initialization is carried out by using the resistance difference value ΔR determined from equation (1) (t=0) or temperature difference value ΔT (t=0) multiplied by the exponential function. ΔR(t0+1)=exp(−dt / τ)∗ΔR(t=0) or ΔT(t0+1)=exp(−dt / τ)∗ΔT(t=0).

[0036] The time constant τ is a value that must be determined once for each glow plug 2 before use and is stored in the engine control unit 7. The parameter -dt specifies the time period of thermal relaxation (starting with t(0)) at which the resistance value ΔR(t 0+1 ) was determined). Thus, the starting value ΔR(t 0+1 ), which is inserted into the function (2) and thus the first modeled temperature value T mod This modeled temperature value is processed as the actual temperature value in the glow plug control system (block 104).

[0037] During the heating phase, the resistance value ΔR(t k ) k times, distributed over the entire heating phase, for example, every 100 ms, by multiplying the last calculated resistance value by the exponential function in block 103. This results in: ΔR(tk)=exp(−dtK / τ)∗ΔR(tk−1) or when converting the resistance values into a temperature ΔT(tk)=exp(−dtK / τ)∗ΔT(tk−1).

[0038] Each resistance value ΔR(t k ) or temperature value ΔT(t k ) is then used in block 104 to determine the temperature T mod for the given time period t K to be calculated and used as the actual temperature value in the control during the heating phase.

[0039] The described model represents the unsteady temperature curve very well both in still air and when starting the diesel engine or when idling and can therefore be used advantageously for controlling the glow temperature of the glow plug 2 in the heating phase.

Claims

[1] Method for regulating or controlling the temperature of a glow plug in a heating phase of the glow plug (2), in which a temperature value is determined as a function of a resistance of the glow plug (2), wherein the heating phase follows a preheating phase, wherein during the preheating phase the cold glow plug (2) is subjected to a heating voltage which is higher than the operating voltage provided for the glow plug (2), whereby a non-stationary temperature profile is formed in the glow plug (2), characterized by that the temperature value (T mod ) depending on a measured resistance (R mess ) and a calculated resistance value (ΔR(t K )) it is determined that the calculated resistance (ΔR(t K )) to determine the temperature value (T mod) during the transient temperature profile within the glow plug (2) is calculated using a physical model, so that the temperature value (T mod ) is determined at several time intervals (k), whereby the calculated resistance value (ΔR(t K )) changes depending on the previous time intervals (k-1), that the calculated first resistance value (ΔR(t 0+1 ))with a starting value (ΔR(t t=0 )) is initialized so that the starting value (ΔR(t T=0 )) from a difference of a resistance (R t=30 ), which is determined once based on a homogeneous temperature distribution in the glow plug, and a resistance detected after the preheating phase (R push(t=0 )), where the calculated resistance value (ΔR(t K )) is determined as a function of a decreasing exponential function, where the exponents depend on the thermal relaxation time (t K) and a time constant (τ) and that the time constant (τ) is determined once for the respective glow plug (2) used. [2] Method according to claim 1, characterized by that the resistance value (ΔR(t K-1 )) the starting point for calculating the next resistance value (ΔR(t K )) in the next time period (k). [3] Method according to claim 1, characterized by that the resistance (R mess ) of the glow plug (2) to form the temperature value (T mod ) is measured after the preheating phase has been completed. [4] Method according to claim 1, characterized by that the measured resistance (R mess ) is determined from a voltage and a current which are determined by measuring a voltage applied to the glow plug (2) and a current flowing through the glow plug (2). [5] Method according to claim 1 characterized by that after the heating phase of the glow plug (2), in which a stationary temperature profile has been established in the glow plug (2), the temperature control is determined as a function of a measured resistance value which represents the temperature of the glow plug (2).

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